Erik Dietzenbacher is Associate Professor of International Economics and Business at the University of Groningen, The Netherlands. He is co-editor of Input-Output Analysis: Frontiers and Extensions (with Michael L. Lahr, 2001), Input-Output Analysis (three volumes, with Heinz D. Kurz and Christian Lager, 1998) and is currently editor of Economic Systems Research, the official journal of the International Input-Output Association. Michael L. Lahr is Associate Research Professor at the Center for Urban Policy Research, Rutgers University, New Jersey. He is co-editor of Input-Output Analysis: Frontiers and Extensions (with Erik Dietzenbacher, 2001) and Regional Science Perspectives in Economics: A Festschrift in Memory of Benjamin H. Stevens (with Ronald E. Miller, 2001).